Here it is the clue given in pottermore potions puzzle section , and find the answer is in the end of this article
Danger lies before you, while safety lies behind,
Two of us will help you, whichever you would find,
One among us seven will let you move ahead,
Another will transport the drinker back instead,
Two among our number hold only nettle wine,
Three of us are killers, waiting hidden in line.
Choose, unless you wish to stay here for evermore,
To help you in your choice, we give you these clues four:
First, however slyly the poison tries to hide
You will always find some on nettle wine’s left side;
Second, different are those who stand at either end,
But if you would move onwards, neither is your friend;
Third, as you see clearly, all are different size,
Neither dwarf nor giant holds death in their insides;
Fourth, the second left and the second on the right
Are twins once you taste them, though different at first sight.
(article of How to unlock pottermore potion puzzle chapter 16, it is the tips tricks tips to click it)you see the answer in picture above , yes it is blue and purple, that is the answer for pottermore potion puzzle,
but how to click it?
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